1. Field of the Invention
The present invention relates generally to a technology for reselecting an antenna in a cellular mobile communication system, and in particular, to a technology for reselecting a plurality of antennas of base stations connected to a mobile station as the mobile station shifts from one place to another.
2. Description of the Related Art
The conventional mobile communication system provides a voice-oriented service, and chiefly depends on channel coding in order to overcome deterioration in channel quality. However, due to an increase in demand for high-quality multimedia service that enables users to communicate with anyone, anytime, anywhere, the conventional voice service is evolving into a data service and there is a demand for a next generation radio transmission technology for transmitting the increased amount of data at a higher data rate and at a lower error rate. In particular, importance of high-speed data transmission in a forward link having the greater amount of required data is ever increasing.
A mobile communication environment deteriorates the reliability of the signals due to fading, shading effect, propagation attenuation, noise, and interference. A fading phenomenon due to multiple paths brings about significant signal distortion caused by the sum of signals having different phases and sizes, which are received through different paths. The fading effect is one of the difficulties that should be overcome in order to achieve a high-speed data communication, and extensive researches is being conducted to overcome the wireless channel characteristics and utilize the features. As a result, a Multiple Input Multiple Output (MIMO) technology using a plurality of transmission and reception antennas has been proposed.
In a cellular mobile communication system using the multiple antennas, unlike in the conventional cellular mobile communication system, a mobile station and a base station, both of which use a plurality of antennas, can exchange data with each other at a higher speed without increasing a bandwidth of the system.
Even in the cellular mobile communication system using multiple antennas, like in the conventional cellular mobile communication system in which a mobile station uses a single antenna, performance of a channel formed between a mobile station and a base station varies due to the movement of the mobile station, and a need for forming a new channel to another antenna occurs as the mobile station moves from one cell to another, or if channel quality is to be adjusted. The cellular mobile communication system using multiple antennas, as a base station has a plurality of antennas even in a single cell, should occasionally reselect antennas according to time-varying channel performance. For example, even when a mobile station moves between sectors in a cell divided by the plurality of antennas of the base station, an antenna should be reselected for the same base station.
In addition, when a mobile station moves from a current cell (serving cell) to another cell (target cell), the mobile station in an overlapping region between the cells may connect with both an antenna of a serving base station and an antenna of a target base station. In this case, it is difficult to reconfigure a channel with the conventional handoff scheme.